The present invention relates to a separating element for separating the bottom part of an electrolytic tank from the rest of the tank space in connection with removing the solids settled on the bottom of the tank, which separating element can be installed in the electrolytic tank and removed therefrom along a path arranged in the electrolytic tank by means of support and control members.
In electrolytic processes, metals such as copper, nickel and zinc, are precipitated on the surfaces of cathodes located in the electrolytic tank, starting either with metal anodes that are dissolved into the electrolyte present in the electrolytic tank, or with metal ions that are already dissolved into the electrolyte. However, all solids are not precipitated onto the cathode surfaces, for example precious metals and solid impurities present in the electrolyte. Therefore on the bottom of electrolytic tanks, there are accumulated, along with the metal refining process, various solids that must from time to time be removed from the tank, for instance because said solids contain valuable ingredients, such as precious metals, or because a thicker solids accretion threatens the purity of the cathode obtained from the electrolytic process.
Usually the solids accumulated in the electrolytic tank are at least partly very finely divided and only somewhat heavier than the electrolyte, wherefore it is difficult to separate the solids from the electrolyte. During the electrolytic process, the circulation of the solids from off the bottom of the electrolytic tank is very harmful, because in that case there is a particularly high risk that the solids proceed onto the cathode, and this would essentially weaken the purity of the metal to be produced.
The removal of the solids accumulated on the bottom of an electrolytic tank usually requires that the whole electrolytic process must be interrupted, which reduces the efficiency per time, i.e. the productivity of the electrolytic plant. Hence the removal of solids must be arranged so that it forms part of the process of replacing the electrodes, i.e. anodes and cathodes; this, however makes the replacement process complicated and slow, and also restricts the removal of solids to take place in the rhythm dictated by the process of replacement. Moreover, a remarkable amount of the electrolyte must be first removed from the tank and then fed back therein, which generally leads to harmful effects in the electrolyte quality and causes a lot of extra work. Into the solids treatment system, there also flows a remarkable amount of electrolyte, which must be replaced with new and may be harmful in the further treatment of the solids. Moreover, the manual washing of the electrolytic tanks makes the process clearly more labor-intensive and subjects the employees to various health hazards, among others owing to the effects of the ingredients contained in the splashes and spray emanating from the tank. In addition, owing to the personnel required by the washing of the tanks, the automatization of the electrode treatment is often nearly impossible, which further increases the labor demand in an electrolytic plant.
From the international patent application WO 99/11841, there is known a separating element for separating the bottom part of an electrolytic tank from the rest of the tank space in connection with the removal of the solids settled on the tank bottom. In said publication, in the electrolytic tank there are arranged support and control members that form the trajectory of the separating element, so that the separating element can be placed in the electrolytic tank and removed therefrom through a space provided in between at least one end wall and the electrode placed nearest to said end wall. In the arrangement according to said publication, the separating element consists of several, flexibly interconnected structure elements that enable the bending of the separating element when shifting from the vicinity of the end wall to the vicinity of the electrolytic tank bottom. The structure specified in said publication is complicated and troublesome to manufacture. In addition, in between the elements of the structure, there may accumulate impurities that are harmful for the operation of the separating element. Moreover, the known separating element, described in said publication, is also difficult to keep clean.
The object of the present invention is to eliminate some of the drawbacks of the prior art and to achieve a novel separating element for electrolytic tanks that is new in structure and more efficient in operation. The essential novel features of the invention are apparent from the appended claims.
The separating element according to the invention comprises a flexible wall element and support members arranged in said wall in order to prevent excessive bending of the wall element at least in one direction. By means of the structure according to the invention, there is achieved a simple and uniform separating element that is secure in operation, to be used in connection with the removal of solids settled in an electrolytic tank. Owing to the flexibility of the separating element, the trajectory of the separating element can be designed to proceed in a desired fashion, for example from an essentially vertical direction near the end wall of the electrolytic tank to an essentially horizontal direction near the bottom wall of the electrolytic tank.
According to the invention, the separating element comprises at least a first set of support members arranged in succession mainly in the motional direction of the separating element. The first set of support members typically reinforce the flexible wall element of the separating element and tend to keep it straight, at the same time allowing bending according to the desired trajectory.
Moreover, the separating element comprises at least another set of support members arranged in the wall element, essentially transversally mainly with respect to the motional direction of the separating element. The transversal support members reinforce the wall element in the direction transversal to the motional direction. The transversal support members can also be used as pulling members when moving the separating element by an actuator, such as a drive wheel.
The separating element according to the invention comprises at least a third set of support members, arranged on the opposite side of the wall element with respect to the first longitudinal support members, said third set of support members being arranged in succession, mainly in the motional direction of the separating element, in order to prevent an excessive bending of the wall element at least in one more direction. The third set of support members is arranged to prevent the bending of the wall element with a too short bending radius when moving the separating element. Preferably the support members include restricting members, such as brackets, that keep the bending radius in the desired magnitude. The uniform wall element forms a compact surface and is easy to keep dean